An exemplary article of footwear, such as a shoe, is described for background purposes. A typical shoe comprises an upper and a sole structure. The sole structure, in turn, may comprise a midsole and an outsole. While a separate midsole and outsole are discussed, it is contemplated that the sole structure may be formed such that the midsole and the outsole are merely regions of a commonly formed structure. For reference purposes, an exemplary shoe may be divided into three general regions or areas: a forefoot or toe region, a midfoot region, and a heel region. The shoe also comprises a lateral side and a medial side. The lateral side generally extends along a lateral side of a user's foot when in an as-worn configuration. The medial side extends along a medial side of the user's foot when in an as-worn configuration. The lateral side and the medial side are not intended to demarcate specific areas of the shoe. Instead, they are intended to represent general areas of the shoe that are used for reference purposes for the following discussion. For example, the medial side and the lateral side may converge near the toe region at respective sides of a toe box. Similarly, it is contemplated that the medial side and the lateral side may also converge at respective sides of the heel region. Therefore, depending on the shoe design and construction, the terms medial, lateral, toe, heel, and the like generally refer to a proximate location and may not be limiting.
The upper portion of an article of footwear is generally secured to the sole structure and defines a cavity for receiving a foot. As mentioned above, the sole structure may comprise the outsole and the midsole. The outsole forms a ground-engaging surface of the sole structure. The midsole is generally positioned between the upper and the outsole. The outsole and/or the midsole may be formed of conventional materials, such as rubber, leather, or a polymer foam material (polyurethane or ethylene-vinyl acetate, for example). The outsole may be integrally formed with the midsole, or the outsole may be attached to a lower surface of the midsole.
Components of a shoe, such as a midsole and an outsole, may be joined together with an adhesive. In traditional examples, the adhesive may be activated by a conventional oven that heats the combination of materials (e.g., components and adhesive) to a sufficient temperature to activate the adhesive. However, raising the temperature of the components to get the adhesive to a sufficient temperature may affect the components (e.g., deform, burn, and the like) in an undesirable manner. Similar, components of footwear may be formed or molded in a tool that is exposed to traditional heat sources. The use of a traditional heat source (e.g., conduction, radiation) may be inefficient as it also heats the tooling and is indiscriminate as to the materials being heated.